Mullen was assigned to Company B, 2nd Battalion, 5th Special Forces Group (Airborne), Fort Campbell, Ky., as an assistant detachment commander for a Special Forces Operational Detachment-Alpha (ODA), or A-team. He was deployed in support of Operation Enduring Freedom-Afghanistan. This was Mullen’s sixth deployment in support of an overseas contingency operation.

Mullen enlisted in the Army in November, 1995, as an Infantryman. Upon completion of basic training and advanced individual training, Mullen was assigned to 3rd Bn., 327th Infantry Regiment, 101st Airborne Division (Air Assault). After successful completion of the Basic Airborne Course at Fort Benning, Ga., he was assigned to 1st Bn., 325th Airborne Infantry Regiment, 82nd Airborne Division, Fort Bragg, N.C. In March 2001, Mullen was assigned to 1st Bn., 503rd Infantry Regiment, 2nd Infantry Division, Camp Casey, Republic of Korea. In April 2002, Mullen was assigned to instruct at the Basic Airborne and Pathfinder courses at Fort Benning, Ga.

Mullen volunteered for the Special Forces Assessment and Selection Course and completed the Special Forces Qualification Course in April 2007.

He was assigned to Co. A, 2nd Bn., 5th SFG (A) as a medical sergeant and later became the senior medical sergeant for the company. Mullen spent two years on a Special Forces team until his selection as the company operations sergeant. After a successful deployment as the company operations sergeant in support of Operation Iraqi Freedom, Mullen was assigned as the senior medic for a Special Forces team in Company A. Mullen deployed again to in support of OIF. Mullen was a member of the first battalion within the U.S. Army Special Forces Command (A) qualified to conduct Unconventional Warfare. Mullen additionally deployed to the Kingdom of Saudi Arabia in support of Special Operations Command – Central requirements.

Mullen was selected to attend the Warrant Officer Technical and Tactical Certification Course; graduating as a Warrant Officer in November 2012.

His awards and decorations include the Bronze Star Medal with oak leaf cluster, Meritorious Service Medal with oak leaf cluster, Army Commendation Medal with two oak leaf clusters, the Joint Service Achievement Medal, Army Achievement Medal with seven oak leaf clusters, the Good Conduct Medal with four knots, the National Defense Service Medal, the Afghanistan Campaign Medal with two campaign stars, the Iraq Campaign Medal with three campaign stars, the Global War on Terrorism Expeditionary Medal, the Global War on Terrorism Service Medal, the Korea Defense Service Medal, the Armed Forces Service Medal, Noncommissioned Officer Professional Development Ribbon with numeral “2” device, Army Service Ribbon, Overseas Service Ribbon with one oak leaf cluster, the Army Reserve Component Overseas Training Ribbon, the Joint Unit Meritorious Award, the Army Meritorious Unit Commendation Award with one oak leaf cluster, Special Forces Tab, Combat Infantryman Badge, Expert Infantryman Badge, Pathfinder Badge, Air Assault Badge, Senior Parachutist Badge and the Parachutist Badge.